1. Field of the Invention
The present invention relates to an internal combustion engine of a vehicle, and particularly, to an internal combustion engine with a cavity at a top end of the piston.
2. Description of the Background Art
An internal combustion engine having an intake manifold injector for injecting fuel into an intake manifold of the engine and an in-cylinder injector for injecting the fuel into a combustion chamber of the engine, and configured to stop fuel injection from the intake manifold injector when the engine load is lower than a preset load and to carry out fuel injection from the intake manifold injector when the engine load is higher than the set load, is known.
As a technique related to such an in-cylinder injector of an engine, Japanese Patent Laying-Open No. 2002-115549 discloses a cylinder direct injection spark ignition engine that can prevent a gas flow from being obstructed by a squish flow generated when a piston approaches the top dead center of combustion, and ensure stable combustion at the time of stratified charge and homogeneous combustion. In the cylinder direct injection spark ignition engine, fuel directly injected into a cylinder from a fuel injector is gathered near a spark plug utilizing a gas flow inside the cylinder to cause ignition, whereby combustion is carried out at a lean air-fuel ratio as a whole. The cylinder direct injection spark ignition engine is characterized in its configuration that a clearance between an exhaust side slope of a piston crown surface and a cylinder head is set to be greater than a clearance between an intake side slope of the piston crown surface and the cylinder head, in a range where the fuel injected into a cavity does not flow out of the cavity into the exhaust side.
According to the cylinder direct injection spark ignition engine, as the clearance of the exhaust side is greater than the clearance of the intake side, the squish flow from the exhaust side toward the intake side can be prevented, which would otherwise occur when the piston approaches the top dead center of combustion. The squish flow from the exhaust side toward the intake side may cause deterioration of combustion stability in the stratified charge and homogeneous combustion as it obstructs a gas flow that gathers the injected fuel near the spark plug in the stratified charge combustion, and also obstructs a gas flow that is supplied for forming a homogeneous air-fuel mixture in the homogeneous combustion. As occurrence of the squish flow from the exhaust side toward the intake side is suppressed, deterioration of combustion stability in the stratified charge and homogeneous combustion due to the squish flow can be prevented. Additionally, deterioration of the combustion stability due to the injected fuel being flown out of the cavity and into the exhaust side, when the exhaust side clearance is increased, can also be prevented.
However, the above-described Japanese Patent Laying-Open No. 2002-115549 merely discloses a cylinder direct injection spark ignition engine in which a cavity is provided at the top end of a piston and the thickness of the top end of the piston is uniform. For example, it is silent about the thickness at the back end of the piston around a piston-pin-boss.